Holograms have long been used for security to indicate that a document or product is authentic and to increase the attractiveness of goods such as lottery and entertainment/sporting event tickets, product packaging such as for DVDs, event programs, calendars and magazines. Indeed, methods and apparatuses for creating holographic optical elements on a recording medium, i.e., substrate, to create an overall optical illusion have been known in the art for some time. As is well known, many such existing apparatuses may include an imaging table, such as a platen, on which the substrate is placed, an imaging laser and associated optics. One of the most well known types of holographic imaging apparatus is a split beam holographic imaging apparatus, which splits a laser into two beams, an object beam and reference beam. The object beam is spread, reflected off of an object and directed onto the recording medium. The reference beam travels directly onto the recording medium. When the two laser beams reach the recording medium, their light waves intersect to create an interference pattern on the substrate, thereby producing a holographic image having certain optical effects.
Notably, however, with known systems, the desired holographic image or optical elements are typically imaged as a whole, in an analog fashion, by using a master that creates the holographic design or optical element on the substrate. For example, as shown in FIG. 1, certain prior art imaging apparatuses for creating holographic or other optical effects, such as those disclosed in U.S. Pat. No. 7,298,533, utilize a master to imprint an optical element, such as a Fresnel lens optical element, in the surface of a substrate. As shown in FIG. 1, to produce the optical elements disclosed in, for example, the '533 patent, a circular, generally convex, stepped master is used to imprint a generally concave, circular optical element 10 in the surface of a thick substrate 12. The optical element 10 has a plurality of rings or steps 14 (actually Fresnel lenses) corresponding to the rings/steps of the master, wherein the rings/steps 14 closer to the center of the lens 10 are the deepest from the surface of the substrate 12.
As best shown in FIG. 2, the rings 14 have inclined refractive surfaces 16 that reflect light so as to form images and to create certain optical effects that may be perceived by a viewer. As the master is circular in shape, however, only circular-shaped optical elements may be produced. In order to produce optical elements having other shapes, the circular optical element 10 must be physically cut or shaved down. For example, to produce a triangle-shaped optical element 18, as shown in FIG. 1, the circular optical element 10 must itself be cut into a triangle shape, as indicated by the dashed lines 20. Moreover, if a sheet having optical elements of a variety of shapes or other holographic designs is desired, mechanical recombination, in which one optical element is physically cut and combined with another optical element to produce an integrated holographic pattern or optical image, must be utilized, which suffers from obvious manufacturing and cost drawbacks. Indeed, even when the optical elements within a pattern are all the same, a step and repeat process must be utilized in order to create an overall holographic pattern.
As will be readily appreciated, such step and repeat process, in addition to being more labor intensive and less customizable, leaves a visible line of demarcation between one image and the next. While there are some techniques that may be carried out to lessen the visibility of such lines, all such step and repeat processes invariably leave some form of demarcation or recombine lines in the final pattern.
Accordingly, while known holographic imaging apparatuses utilizing physical imprinting or surface relief are effective to a certain degree, such apparatuses are limited in the shape and intricacy of holographic images and optical elements that can be produced.
It has been discovered, however, that by imaging in a digital fashion, i.e., pixel by pixel, certain advantages such as the ability to create holographic images and optical elements of any shape and size may be realized.